Semen Frank (1877–1950) was one of the first and most ardent advocates of the ontological argument in the twentieth century. He proposed an original interpretation of the ontological argument based on its analogy to Descartes’ Cogito. Frank believed that it is possible to develop Cogito ergo sum into Cogito ergo est ens absolutum. In this paper, I analyze his version of the ontological argument. First, I propose a simple reconstruction of his reasoning, paying attention to its hidden premise. Second, departing (...) from the classical logical interpretations of Descartes’ argument, I show that for Frank the claim that God exists had the same logical properties as Cogito. As a result, it seems that his argument was formally correct, though based on a premise which could hardly be convincing for a non-believer. This should not be surprising, however, since Frank, as most Russian religious philosophers, was not interested in the project of philosophical theology. His main concern was rather the development of philosophy based on religious premises, which might be called “theological philosophy”. (shrink)